Less oxygen dissolved in the water is often referred to as a ‚??dead zone‚?Ě (in red above) because most marine life either dies, or, if they are mobile such as fish, leave the area. / NOAA

by Dan Vergano, USA TODAY

by Dan Vergano, USA TODAY

Environmental biologists foresee a record-size "dead zone" for the Gulf of Mexico this summer, a New Jersey-sized patch of water deadly to marine life, federal officials announced on Tuesday.

Seen every year off the Texas and Louisiana coasts, the zone forms largely because of fertilizer runoff from the corn belt flowing down the Mississippi, where the nutrients spur the growth of algal blooms that remove oxygen from the water in the Gulf. The especially large size this year of the predicted zone, perhaps 8,500 square miles, appears to be tied to Midwestern floods that washed more nutrients into the river.

"The estimate is this will be the largest zone ever, unless there is a storm that stirs up the water," says researcher R. Eugene Turner of Louisiana State University in Baton Rouge, who was one of the modelers on which the National Oceanic and Atmospheric Administration and other agencies based their prediction. "Even if there is a storm it is going to be a very large zone," Turner says.

Records have been kept on the summer dead zone in the Gulf since 1985. Last year's zone was one of the smallest on record, as a drought prevented runoff carrying as much fertilizer into the Mississippi River.

The prediction is better for the Chesapeake Bay, where estimates are for a smaller-than-average dead zone there, similar to last year. Improved conditions in the bay appear tied to improved water-treatment facilities in the region, suggests water-quality expert Michael Woodside of the U.S. Geological Survey (USGS), resulting in 30% fewer nutrients than average flowing into the estuary. That means more crabs, oysters and fish there.

Turner was critical of inaction on reducing the amount of fertilizer running into the Gulf, some 153,000 metric tons of nutrients in May, nearly three times as much as last year. He notes that a federal, state and tribal agreement aims to cut the average size of the dead zone in half by 2015, "and I don't see any sign of that happening," he says.

With corn prices high, it appears that farmers this year decided in favor of applying larger amounts of fertilizer, suggests Jerad Bales, USGS associate director for water. "A lot of the contribution to nutrient flow comes from groundwater, which can take years to reach the river," Bales says. "That means even if we take steps to cut nutrients, this could still be a growing problem for years."

The dead zones typically break apart in the fall, as waves and winds re-oxygenate the affected patches of water.